1. Field of the Invention
The present invention relates to a method of recording and reproducing images produced by an electron microscope, and more particularly to a method of recording electron microscope images with high sensitivity and of reproducing the recorded electron microscope images in the form of electric signals in order to allow the images to be processed in various ways.
2. Description of the Prior Art
There are known electron microscopes for obtaining a magnified image of a specimen by deflecting a beam of electrons transmitted through the specimen with an electric or magnetic field. As is well known, the electron beam having passed through the specimen forms a diffraction pattern on the rear focal plane of the objective lens, and the diffracted beams interfere with each other again to produce the magnified image of the specimen. The magnified specimen image can be observed as a scattered-light image by projecting the image onto a screen with a projector lens. Alternatively, the rear focal plane of the objective lens may be projected for enabling the user to observe the magnified diffraction pattern of the image. Where an intermediate lens is positioned between the objective lens and the projector lens, the magnified scattered-light image or the diffraction pattern may be produced selectively as desired by adjusting the focal length of the intermediate lens.
The magnified image or the diffraction pattern (hereinafter referred to collectively as a "transmitted electron-beam image") may be observed in different manners. For example, one general practice has been to place a photographic film on the image formation plane for exposure to the transmitted electron-beam image. According to another design, an image intensifier is employed to amplify the transmitted electron-beam image for projection. The use of photographic films is however disadvantageous in that their sensitivity to electron beams is low and the process of developing the films is complex. The image intensifier also has drawbacks in that the images produced thereby have poor sharpness and are likely to become distorted.
Transmitted electron-beam images are often processed to make them more easier to see. Specifically, the transmitted electron-beam images are subject to various signal processing modes such as tone processing, frequency emphasis, density processing, subtractive processing, and additive processing. The images are also processed to reconstruct three-dimensional images by Fourier analysis, digitize the images, and measure particle diameters. The diffraction patterns are also processed to analyze crystal information and find lattice constants, dislocations, and lattice defects. For such image and diffraction pattern processing, it has been customary to convert the electron microscope image on a developed photographic film into an electric signal with a microphotometer, convert the electric signal into a digital signal, and then process the digital signal with a computer. This process has proven unsatisfactory since it is quite complex.